The cylinders of bowl-mill crushers are oriented in relation to the bowl in such a way as to ensure that their total force will act on the material being crushed no matter how deep it is piled in the bowl. To establish the particular force that is to be exerted on the material in order to crush it, the cylinders are forced against the bowl at a particular pressure, the extent of which depends on how difficult the material is to crush. The pressure is maintained constant during the operation. When crushing difficult-to-crush coal with a low Hardgrove number and with a high percentage of fines in the rough-coal composition, the crusher may begin running erratically at certain stages and develop a considerable amount of vibration accompanied by noise. This erratic operation cannot be corrected satisfactorily by redesigning the crusher.
The object of the invention is to provide a method of controlling a bowl-mill crusher that will allow it to run quitely in all operating situations.
How smoothly a bowl-mill crusher runs depends on, among other factors, how full it is, a situation that is expressed in a loss of primary-air pressure between the intake into the crusher and the outlet from the burner or in other words in a particular primary-air pressure upstream of the crusher. It has been demonstrated that the air turbulence increases in spurts once the primary-air pressure exceeds a particular level. With this discovery as a point of departure accordingly, a method of controlling a crusher is proposed wherein the pressure of the cylinders is varied when the load-dependent primary-air pressure deviates from a prescribed level. This method can be exploited to drive a bowl-mill crusher quietly.